Brewing sencha without a thermometer
Sencha turns bitter when the water is too hot. Most leaf does well around 70 to 80 degrees Celsius, and you can get there without any gadget by pouring boiled water into each cup first, then from the cups into the pot. Every transfer takes off some heat.
Steep for about a minute, then pour every last drop out. Leaves left sitting in water keep extracting and spoil the next round.
The second and third infusions
The leaves have opened by the second pour, so it needs only a few seconds. The third can take a little more time and slightly hotter water. Each one tastes different, which is half the pleasure.
Choosing a pot
A small side-handled kyusu with a fine strainer is ideal. Its size matters more than its price: a pot for two cups lets you serve the whole infusion at once.